Backstory can be shown in story, implied, slowly revealed, or not mentioned at all, but when the author does have it, it’s used to deepen a character and explain why they act the way they do now. However, it has to make sense within their characterization, lest your audience be left scratching their heads.

For example, a character who was beaten and left for dead while people walked by and do nothing isn’t going to be a very idealistic person unless someone or something turns them away from their (justified) cynicism. On the other hand, a character who’s lived a happy life where everyone got along probably isn’t going to be all that cynical, though they may be shocked when disagreement ends in violence.

Creating your character’s backstory

A good method for creating a character’s backstory, I’ve found, is to create the character first, and work backwards through their life, trying to figure out what made them the way they are.

Writing Adam, who is very stoic, despite having strong emotions, I discovered that a good way to explain his unwillingness to actually show feeling was to have some long period where showing emotion would be harmful, so I gave him something he hate hated getting, in this case pity, piled it on him for about a year,and made him react very badly to it. This, in his slightly twisted mind would make him associate showing emotions with making things worse for himself. Of course, I needed a reason for him to constantly be shown pity, so I killed his parents in a fantastic fireball, and had a recently discovered sibling slowly dying of cancer.

Honestly, if my characters knew I was purposefully making their lives hard, they would find some way to put two in my chest.

An alternative method would be to create the backstory first, then work your way forward, creating their characterization based on that. This is a far better method in revenge plots and such.

Ultimately, All I can say is find what works best for creating your character’s backstory, and run with it,

Rape as backstory

Also, though it is tempting to use rape as a backstory, my advice is don’t, unless you know and understand the psychological effects of rape (which I will be the first to admit that I don’t, though I have a story idea that relies on a lot of rape as backstory. It isn’t a happy story), so that you don’t embarrass yourself or worse, belittle rape victims. It is a traumatic experience, and one that should be treated with the greatest of care when you’re writing it in fiction.